I/O Ports

1. IO PORTS
Session 4
SURYAPRAKASH S
suryaprakash.vsm@gmail.com
The resource for the PPT is made from variety of Books and online
PPT that were available in Internet. The Purpose of the PPT is made
for the Classroom Teaching.

2. Agenda
• IO PORT TYPES AND EXAMPLES
12-02-2019 suryaprakash.vsm@gmail.com 2

3. I/O Ports
to receive the bytes from external peripheral(s)
[or device(s) or processor(s) or controllers] for
reading them later using instructions executed on
the processor or
to send the bytes to external peripheral or device
or processor using instructions executed on
processor

4. A Port connects to the processor using address
decoder and system buses
The processor uses the addresses of the port-
registers for programming the port functions or
modes, reading port status and for writing or
reading bytes.
I/O Ports

5. Example
• SI serial interface in 8051
• SPI serial peripheral interface in 68HC11
• PPI parallel peripheral interface 8255
• Ports P0, P1, P2 and P3 in 8051 or PA, PB,
• PC and PD in 68HC11
• COM1 and COM2 ports in an IBM PC

6. Types of Serial ports
Synchronous
Serial Input
Synchronous
Serial Output
Asynchronous
Serial UART
input
Asynchronous
Serial UART
output
Both as input
and as
output, for
example,
modem.

7. TYPES OF PARALLEL PORTS
Parallel port one
bit Input
Parallel one bit
output
Parallel Port
multi-bit Input
Parallel Port
multi-bit Output

8. Synchronous Serial Input Example
Inter-processor data transfer, reading from CD or hard disk, audio
input, video input, dial tone, network input, transceiver input, scanner
input, remote controller input, serial I/O bus input, writing to flash
memory using SDIO (Secure Data Association IO based card)

9. Synchronous Serial Input
The sender along with the serial bits also sends the clock pulses SCLK (serial clock)
to the receiver port pin. The port synchronizes the serial data- input bits with
clock bits. Each bit in each byte as well as each byte in synchronization
Synchronization means separation by a constant interval or phase difference. If
clock period = T, then each byte at the port is received at input in period = 8T.
The bytes are received at constant rates. Each byte at input port separates by 8T
and data transfer rate for the serial line bits is (1/T) bps. [1bps = 1 bit per s]

10. Serial data and clock pulse-inputs
On same input line − when clock pulses either encode or modulate
serial data input bits suitably. Receiver detects the clock pulses and
receives data bits after decoding or demodulating.
On separate input line − When a separate SCLK input is sent, the
receiver detects at the middle or +ve edge or –ve edge of the clock
pulses that whether the data-input is 1 or 0 and saves the bits in an
8-bit shift register. The processing element at the port (peripheral)
saves the byte at a port register from where the microprocessor
reads the byte.

11. Master output slave input (MOSI) and Master input
slave output (MISO)
MOSI when the SCLK is sent from the sender to the receiver and
slave is forced to synchronize sent inputs from the master as
per the inputs from master clock.
MISO when the SCLK is sent to the sender (slave) from the
receiver (master) and slave is forced to synchronize for sending
the inputs to master as per the master clock outputs.
Synchronous serial input is used for inter-processor transfers,
audio inputs and streaming data inputs.

12. Synchronous Serial Output Device (Device Serial Bits
and synchronisation clock signal at a port output)
Example Synchronous Serial Output : Inter-processor data
transfer, multiprocessor communication, writing to CD or hard
disk, audio Input/output, video Input/output, dialer output,
network device output, remote TV Control, transceiver output,
and serial I/O bus output or writing to flash memory using SDIO

13. Synchronous Serial Output
• Each bit in each byte sent in synchronization with a clock.
• Bytes sent at constant rates. If clock period= T, then data transfer rate
is (1/T) bps.
• Sender either sends the clock pulses at SCLK pin or sends the serial
data output and clock pulse-input through same output line with
clock pulses either suitably modulate or encode the serial output bits.

14. Synchronous serial output using shift register
• The processing element at the port (peripheral) sends the byte
through a shift register at the port to where the microprocessor
writes the byte.
• Synchronous serial output is used for inter-processor transfers, audio
outputs and streaming data outputs.

15. Synchronous Serial Input/Output

16. Synchronous Serial Input/Output
• Each bit in each byte is in synchronization at input and each bit in
each byte is in synchronization at output with the master clock output
.
• The bytes are sent or received at constant rates. The I/O’s can also be
on same I/O line when input/output clock pulses either suitably
modulate or encode the serial input/output, respectively. If clock
period = T, then data transfer rate is (1/T) bps.
• The processing element at the port (peripheral) sends and receives
the byte at a port register to or from where the microprocessor writes
or reads the byte

17. Asynchronous Serial input RxD at UART COM
Port

18. Asynchronous Serial port line D RxD (receive
data).
• Does not receive the clock pulses or clock information along with the
bits.
• Each bit is received in each byte at fixed intervals but each received
byte is not in synchronization.
• Bytes separate by the variable intervals or phase differences
• Asynchronous serial input also called UART input if serial input is
according to UART protocol

19. Example Serial Asynchronous Input
• Asynchronous serial input
is used for keypad inputs
and modem inputs in
computers
• Keypad controller serial
data-in, mice, keyboard
controller, modem input,
character send inputs on
serial line [also called
UART (universal receiver
and transmitter) input
when according to UART
mode]

20. UART protocol serial line format
• Starting point of receiving the bits for each byte is indicated by a line transition from 1 to
0 for a period = T. [T −1 called baud rate.]
• If sender’s shift-clock period = T, then a byte at the port is received at input in period =
10.T or 11.T due to use of additional bits at start and end of each byte.
• Receiver detects n bits at the intervals of T from the middle of the start indicating bit.
The n = 0, 1, …, 10 or 11 and finds whether the data-input is 1 or 0 and saves the bits in
an 8-bit shift register.
• Processing element at the port (peripheral) saves the byte at a port register from where
the microprocessor reads the byte.

21. Asynchronous Serial Output
• Asynchronous output serial port line TxD (transmit data).
• Each bit in each byte transmit at fixed intervals but each output byte
is not in synchronization separates by a variable interval or phase
difference). Minimum separation is 1 stop bit interval

22. TxD
• Does not send the clock pulses along with the bits.
• Sender transmits the bytes at the minimum intervals of n.T.
Bits receiving starts from the middle of the start indicating
bit,
• n = 0, 1, …, 10 or 11 and sender sends the bits through a 10
or 11 -bit shift register.
• The processing element at the port (peripheral) sends the
byte at a port register to where the microprocessor is to
write the byte.
• Synchronous serial output is also called UART output if serial
output is according to UART protocol

23. Example Serial Asynchronous Output
• Output from modem, output for printer, the output on a serial line
[also called UART output when according to UART]

24. Half Duplex
Half duplex means as follows: at an instant
communication can only be one way (input or
output) on a bi-directional line.
An example of half-duplex mode─ telephone
communication. On one telephone line, the talk
can only in the half-duplex way mode.
Full Duplex
Full duplex means that at an instant, the
communication can be both ways. An example of
the full duplex asynchronous mode of
communication is the communication between
the modem and the computer though TxD and
RxD lines or communication using SI in modes 1,
2 and 3 in 8051

25. Parallel Port single bit input
• Completion of a revolution of a wheel,
• Achieving preset pressure in a boiler,
• Exceeding the upper limit of permitted weight over the pan of an
electronic balance,
• Presence of a magnetic piece in the vicinity of or within reach of a
robot arm to its end point and
• Filling of a liquid up to a fixed level.

26. Parallel Port Output- - single bit
• PWM output for a DAC, which controls liquid level, or temperature, or
pressure, or speed or angular position of a rotating shaft or a linear
displacement of an object or a d.c. motor control
• Pulses to an external circuit
• Control signal to an external circuit

27. Parallel Port Input- multi-bit
• ADC input from liquid level measuring sensor or temperature sensor
or pressure sensor or speed sensor or d.c. motor rpm sensor
• Encoder inputs for bits for angular position of a rotating shaft or a
linear displacement of an object

28. Parallel Port Output- - multi-bit
• LCD controller for Multilane LCD display matrix unit in a cellular
phone to display on the screen the phone number, time, messages,
character outputs or pictogram bit-images for display screen or e-mail
or web page
• Print controller output
• Stepper-motor coil driving bits

29. Parallel Port Input- - Output
• PPI 8255
• Touch screen in mobile phone

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